A bent molecule has a general formula of AX₂E or AX₂E₂
Based on VSEPR theory, water (H₂O) molecule is composed of 1 central atom (oxygen) with 2 lone pairs, attached to 2 hydrogen atoms, has a bent geometry.
Alternative C is the correct answer.

The lowest intermolecular force is London dispersion.
Dispersion forces increase with increasing molecular weight.
From the given compounds, methane has the smallest molecular weight, therefore the smallest intermolecular force.
Alternative D is the correct answer.

Tetrahedral structure has AX₄ as a general formula.
From the given compounds, CH₄ with one central atom (carbon), attached to 4 hydrogen atoms, has AX₄ as a general formula. Then, CH₄ has a tetrahedral structure.
Alternative D is the correct answer.

Hydrogen bonding occurs only when hydrogen atoms are covalently attached to one of the most electronegative elements O, F or N.
Notice that each water molecule can potentially form four hydrogen bonds with surrounding water molecules: two with the hydrogen atoms and two with the oxygen atoms.
Water molecules are held together by hydrogen bonding.
Alternative C is the correct answer.

Molar mass is the mass in grams of one mole of a substance.
The unit of molar mass is grams per mole, abbreviated as g/mol.

The molality of a solution is equal to the moles of solute divided by the mass of solvent in kilograms.
The unit for molality is mol/kg

The molarity of a solution is equal to the moles of solute divided by the volume of solution in liters.
The unit of molarity is mol/L

The molal boiling-point elevation constant is a constant that is equal to the change in the boiling point for a 1-molal solution of a nonvolatile molecular solute.
Therefore, Degrees Celsius times Kilogram per mole (^°C.kg.mol⁻¹) is a unit of molar boiling-point elevation constant.

A and B are two synthesis reactions. Which one of them is a redox reaction?
Reaction B: C + O₂ → CO₂ is the redox reaction.
The free elements C and O₂ each have an oxidation number of 0.
The product CO₂ has a total oxidation number equal to 0, where O has an oxidation number of -2, which means C in CO₂ has an oxidation number of +4.
The oxidation number of C increases from 0 to +4 indicating oxidation.
The oxidation number of O decreases from 0 to -2, indicating reduction.
Reaction B is the correct answer.

A disproportionation redox reaction is a redox reaction where a single substance can be both oxidized and reduced.
In alternative C:
On the reactant side (a single substance), O has an oxidation state of -1 in H₂O₂, which changes to -2 for the product H₂O (oxygen is reduced), and 0 in the product O₂ (oxygen is oxidized).

A non-redox reaction is a reaction where the oxidation number for each element remain unchanged in the reaction.
In Alternative A: on the reactant side, H⁺ has an oxidation number of +1, O in OH^- has an oxidation number of -2 and H in OH^- has an oxidation number of +1. On the product side, H in H₂O has an oxidation number of +1 and O in H₂O has an oxidation number of -2.
The oxidation number for each element remain unchanged in the reaction → Reaction A is a non-redox reaction.

Increasing the surface area of a reactant increases the frequency of collisions and increases the reaction rate which increases the percent yield of a reaction.
According to the graph, reaction A shows the smallest percent yield hence the smallest surface area.
Reaction C shows the highest percent yield, hence the highest surface area.
Reaction B shows a percent yield greater than reaction A but smaller than reaction C, therefore Reaction B has a greater surface area than A but smaller than C.
When the iron used is in the powdered form, the surface area is the highest → Highest percent yield.
According to the graph, reaction C is the correct answer.

Increasing the surface area of a reactant increases the frequency of collisions and increases the reaction rate which increases the percent yield of a reaction.
According to the graph, reaction A shows the smallest percent yield hence the smallest surface area.
Reaction C shows the highest percent yield, hence the highest surface area.
Reaction B shows a percent yield greater than reaction A but smaller than reaction C, therefore Reaction B has a greater surface area than A but smaller than C.
When the iron used is a block, the surface area is the smallest → Smallest percent yield.
According to the graph, reaction A is the correct answer.

Increasing the surface area of a reactant increases the frequency of collisions and increases the reaction rate which increases the percent yield of a reaction.
According to the graph, reaction A shows the smallest percent yield hence the smallest surface area.
Reaction C shows the highest percent yield, hence the highest surface area.
Reaction B shows a percent yield greater than reaction A but smaller than reaction C, therefore Reaction B has a greater surface area than A but smaller than C.
When the iron used is made from tiny pieces its surface area is smaller than the iron block but greater than the iron in powdered form → According to the graph, reaction B is the correct answer.

In reference to the graph:
The reaction has stopped which means that the volume of gas produced as a function of time remains constant:
phase C.

The total volume of gas produced is 22 cm³.
In phase A: From 0 seconds to 12 seconds, 16 cm³ of gas are produced.
Hence, we can say: In 12 seconds, the reaction rate of gas produced increases by 70 % approximately
( 16 x 100 / 22 )
The reaction rate is the highest at this stage.

In phase B:
From 12 seconds to 50 seconds, 6 cm³ gas are produced.
Hence, we can say: In 38 seconds, the reaction rate increases by 30 % approximately ( 6 x 100 / 22 ).
The reaction starts to slow down at this stage.

For ZnS compound:
1-Name the metal (the cation) as it appears on the periodic table. Zn: zinc
2-For the non-metal (the anion), write the name as it appears on the periodic table and then replace the ending “ur” with “ide”. S: sulfur → S^2-sulfide
Then, ZnS is zinc sulfide.
C is the correct answer.

For ZnSO₃ compound:
1-Name the metal (the cation) as it appears on the periodic table. Zn: zinc
2-Write the name for the polyatomic ion. SO₃^2- : sulfite ion (the anion).
Then, ZnSO₃ is zinc sulfite. A is the correct answer.

For ZnSO₄ compound:
1-Name the metal (the cation) as it appears on the periodic table. Zn: zinc
2-Write the name for the polyatomic ion. SO₄^2- : sulfate ion (the anion).
Then, ZnSO₄ is zinc sulfate. B is the correct answer.

The quantum number 𝑙 is the angular momentum quantum number. It is an integer that defines the shape of the orbital, and takes on the values, 𝑙 = 0, 1, 2, …, 𝑛 – 1. This means that an orbital with 𝑛 = 1 can have only one value of 𝑙, 𝑙 = 0, whereas 𝑛 = 2 permits 𝑙 = 0 and 𝑙 = 1, and so on. The 𝑙 value specifies the shape of the orbital.
Orbitals with the same value of 𝑙 form a subshell. Orbitals with 𝑙 = 0 are called 𝑠 orbitals (or the 𝑠 subshells).
The value 𝑙 = 1 corresponds to the 𝑝 orbitals. The orbitals with 𝑙 = 2 are called the 𝑑 orbitals, followed by the 𝑓-,g-, and h-orbitals for 𝑙 = 3, 4, 5, and so on.
Then, the value of the angular quantum number 𝑙 for the 𝑑 sublevel is 2.
Alternative C is the correct answer.

The lowest energy state an atom can be at is called its ground state. When an electron in an atom has absorbed energy it is said to be in an excited state.
Once the electron in a hydrogen atom absorbs a quantum of energy, the electron becomes excited and "jumps" to an orbit farther from the nucleus.
In other words, it goes up to a higher energy state, it is now in its excited state.
Alternative B is the correct answer

The electron configuration of the element ₉F is: 1s²2s²2p⁵.
The element F has s²p⁵ for its principal energy level 2.
The correct answer should have s²p⁵ configuration for principle energy level 3. From the given elements, ₁₇Cl is the correct answer which has the electron configuration 1s²2s²2p⁶3s²3p⁵.
Alternative D is the correct answer

The electron configuration of an element describes how electrons are distributed in its atomic orbitals.
The given electron configuration 1s²2s²2p⁶3s²3p⁵ shows that the element has a sum of 17 electrons (2+2+6+2+5).
The atom is electrically neutral, number of electrons = number of protons = to the atomic number Z.
In reference to the periodic table, the given electron configuration is for chlorine element (Z=17).
Alternative C is the correct answer

Electrolytes are chemicals that break into ions in water. Aqueous solutions containing electrolytes conduct electricity.
A strong electrolyte conducts electricity very well. Strong electrolytes include the strong acids, strong bases, and most ofthe salts. These chemicals completely dissociate into ions in aqueous solution.
A weak electrolyte conducts electricity a little. Weak electrolytes only partially break into ions in water. Weak electrolytes include weak acids, weak bases, and a variety of other compounds. Most compounds that contain nitrogen are weak electrolytes.
A nonelectrolyte does not conduct electricity. Nonelectrolytes do not break into ions in water. Common examples include sugars, fats, and alcohols.
Column I, lists strong acids → Strong electrolytes
Column II, lists weak acids → Weak electrolytes
Column III, lists alcohol and sugar molecules → nonelectrolytes.
Alternative D is the correct answer.

Both set I and set III contain CO₂ and H₂CS molecular compounds.
CO₂ is attached by 2 double bonds (C=O) and H₂CS is attached by one double bond (C=S) and 2 single bonds (C-H).
Also, O₂ molecule in set III is attached by one double bond (O=O). Therefore, set I and III are incorrect answers.
In set II: Br₂ molecule is attached by one single bond (Br-Br) and SF₂ is attached by 2 single bonds (S-F), N₂H₄ is attached by 5 single bonds (one N-N and 4 N-H) and H₂ is attached by one single bond (H-H).
Therefore, set II contains single covalent bonds only.
Alternative D is the correct answer.

A nonmetal in group 6A has 6 valence electrons in its outermost shell.
These nonmetals have tendency to gain 2 electrons and form ions.
Then, the correct charge for the most common monoatomic ions for a nonmetal in group 6A is 2-.

Ionic compounds generally form between elements that are metals and elements that are nonmetals with sharply different electronegativities.
From the given alternatives, the Ca metal and the F nonmetal in alternative A will produce a compound with ionic bond.
All the other elements in each alternative are nonmetals elements.
Alternative A is the correct answer.

Calcium ion (Ca²⁺) has a mass number of 40 u, number of protons 20, number of neutrons 20 (40-20), number of nucleons 40 (number of protons + number of neutrons) and number of electrons 18 (20-2e^- = 18 electrons).
Chloride ion (Cl^-) has a mass number of 35 u, number of protons 17, number of neutrons 18 (35-17), number of nucleons 35 (number of protons + number of neutrons) and number of electrons 18 (17+1e^- = 18 electrons).
Argon atom (Ar) has a mass number of 40 u, number of protons 18, number of neutrons (number of protons + number of neutrons) 22 (40-18), number of nucleons 40 and number of electrons 18.
All of the three species have the same number of electrons.
Alternative E is the correct answer.

In alternative D, PCl₅ compound is formed through covalent bonding (electron sharing) from one P element and 5 Cl element.
The octet rule reflects that elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. In reference to the periodic table, the element P (Group 5A) has 5 valence electrons and requires 3 electrons to become stable.
The element Cl (Group 7A) has 7 valence electrons and requires 1 electron to become stable.
The P element shares 5 electrons with 5 Cl elements.
Therefore, PCl₅ violates the octet rule.
Alternative D is the correct answer.

Ionic compounds conduct electricity when molten (liquid) or in aqueous solution (dissolved in water), because their ions are free to move from place to place. Ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move.
Compounds that do not produce ions in water cannot conduct electricity. Glucose, is an example of a compound that dissolves in water but does not produce ions.
Sodium chloride solution produce ions in water but sodium chloride in its solid state cannot conduct electricity because ions are fixed in position and cannot move.
Alternative C is the correct answer.

In reference to the trends in periodic table, in general, the atomic radius decreases across a period and increases down a group.
Comparing the elements given in each alternative, Cl element has the smallest radius.
Alternative D is the correct answer.

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
Therefore, alternative A is the correct answer.

Electronegativity increases across a period because the number of charges on the nucleus increases.
As you go down a group, electronegativity decreases because the bonding pair of electrons is increasingly distant from the attraction of the nucleus.
Alternative C is the correct answer.

Metallic character refers to the level of reactivity of a metal. Metallic character decreases as you move across a period in the periodic table from left to right.
This occurs as atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell. Metallic character increases as you move down an element group in the periodic table. In alternative C, in reference to the periodic table, Si element (period 3, Group 4A) has a metallic character greater than P element (period 3, Group 5A) and the latter has a metallic character greater than S element (period 3, Group 6A).
Alternative C is the correct answer.

All phase changes are accompanied by changes in the energy of a system.
Changes from a more-ordered state to a less-ordered state are endothermic.
Changes from a less-ordered state to a more-ordered state are always exothermic.
Condensation is the phase change in which a substance changes from a gas or a vapor to a liquid which means a change from a less-order state to a more-ordered state → Exothermic reaction.
Alternative B is the correct answer

In order for a liquid molecule to escape into the gas state, the molecule must have enough kinetic energy to overcome the intermolecular attractive forces in the liquid.
A given liquid will evaporate more quickly when it is heated.
This is because the heating process results in a greater fraction of the liquid's molecules having the necessary kinetic energy to escape the surface of the liquid.
Therefore, particles with the highest kinetic energy evaporate the fastest.
Alternative D is the correct answer.

A phase change is a physical process in which a substance goes from one phase to another without a change in chemical composition.
Melting is defined as the process of converting a substance from the solid to the liquid state of matter.
Freezing is defined as the process of converting a substance from a liquid to a solid state of matter.
Boiling is defined as a phase transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point.
Evaporation is the process by which a substance changes from its liquid state to its gaseous state. It occurs only from the top most layer of the liquid and is a very slow vaporization process.
Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.It does not involve a phase change.
Alternative C is the correct answer.

The balloon is heated which mean that the temperature increases, then, the volume of the gas increases respectively. Charles’s law states that the volume of a gas is directly proportional to its absolute temperature, assuming the quantity of gas and pressure remain constant.
Alternative C is the correct answer.

As Gay-Lussac’s Law:
P₁ / T₁ = P₂ / T₂ → T₂ = P₂ x T₁ / P₁ = 10.4 x 293 / 8.53 = 357.23 K
Alternative A is the correct answer.

n = C x V = 0.0250 x 1500.10^-3 = 0.0375 mol
n = m / M → m = n x M = 0.0375 X 74 = 2.775 g
Alternative B is the correct answer.

The experiment shows the preparation of a solution starting from a commercial solution. A volume V is transferred from one volumetric flask to another, then, distilled water is added. This set up doesn’t correspond neither to distillation nor to diffusion processes.
Therefore, alternative C is the correct answer.

In reference to the experiment, to prepare the desired solution from a commercial solution, we used 2 volumetric flasks a volumetric pipette and a plastic wash bottle.
Alternative D is the correct answer.

In reference to the figure, step 1 shows that a liquid is withdrawn from the first volumetric flask (an ascending arrow) using a volumetric pipette.
Alternative A is the correct answer.

Step 3 represents the preparation of one solution: dilution of a known volume of a commercial solution by adding distilled water.
Alternative B is the correct answer.

Imbalanced equation: FeBr₃ + H₂SO₄ → Fe₂(SO₄)₃ + HBr
Balanced equation: 2FeBr₃ + 3H₂SO₄ → Fe₂(SO₄)₃ + 6HBr
The sum of the balancing coefficients: 2 + 3 + 1 + 6 = 12
Alternative C is the correct answer.

The overall equation: 2KClO_3(s) → 2KCl_(s) + 3O_2(g) As stoichiometry:
n _(KClO3) / 2 = n_(o2) / 3 → n_(o2) = 3 x n _(KClO3) / 2 = 3 x 0.42 / 2 = 0.63 mol
n_(o2) = m_(o2) / M_(o2) → m_(o2) = n_(o2) x M_(o2) = 0.63 x 32 = 20.16 g
m_{(o2)theoretical} = 20.16 g
m_(o2)actual = 16 g
Yield = m_(o2)actual / m_{(o2)theoretical} x 100 = 16 / 20.16 x 100 = 79.36%
Alternative A is the correct answer.

Preparation of calcium oxide reaction: 2Ca + O₂ → 2CaO As stoichiometry: n _Ca / 2 = n_o2 / 1 = n_CaO / 2
n_Ca / 2 = n_Cao / 2 → n_Ca = n_CaO = 0.2mol
n_o2 / 1 = n_Cao / 2 → n_o2 = 0.2 / 2 = 0.1mol
n_o2 = V / V_m → V_o2 = n_o2 x V_m = 0.1 x 22.4 = 2.24L
Alternative E is the correct answer.

n_Mg = m_Mg / M_Mg = 2.4 / 24 = 0.1 mol → R_Mg = 0.1 / 3 = 0.033
n_H3PO4 = C x V = 1 x 0.03 = 0.03 mol → R_H3PO4 = 0.03 / 2 = 0.015
The limiting reactant is H₃PO₄.
As stoichiometry:
n _H3PO4 / 2 = n _H2 / 3 → n _H2 = 3x0.03 / 2 =0.045 mol
n _H2 = V_H2 / V_m → V_H2 = n_H2 x V_m = 0.045 x 22.4 = 1.008L
Alternative E is the correct answer.

The reaction between an Arrhenius acid and an Arrhenius base is called neutralization and results in the formation of water and a salt.
Alternative B is the correct answer.

The oxidation number is a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction.
HClO₄ is a neutral molecule that has an oxidation number of 0.
H in HClO₄ has an oxidation number of +1.
O in HClO₄ has an oxidation number of -2.
Then, Cl oxidation number in HClO₄ is:
Let x be the oxidation number of Cl,
+1 + x + (4×-2) = 0 → x = + 7
Alternative C is the correct answer.

The titration reaction of a strong acid with a strong base will form a neutral solution with a pH = 7.
Among the alternatives given, and in reference to the acid-base indicators table, bromothymol blue could be properly used (pH range between 6 – 7.6)
Alternative B is the correct answer.

In reference to the color change of bromothymol blue:yellow (acid) to blue (base), the color of the resulting solution obtained at the equivalence point (pH=7) is green.

In reference to item (57), the titration reaction of a strong acid with a strong base will form a neutral solution with a pH = 7 at 25^°C.
Alternative C is the correct answer.

In reference to the acid-base indicators table, pH range of Thymol blue is 8.0-9.6.
This range tells that the pH at the equivalence point will be basic.
This indicator is properly used for the titration of a weak acid and a strong base having a pH at equivalence greater than 7.
Alternative D is the correct answer.

Calcium carbonate is a chemical compound with the formula: CaCO₃, formed by 1 Ca atom, 1 C atom and 3 O atoms.
Molar mass of CaCO₃ = 100 g/mol
Molar mass of Ca = 40 g/mol → %Ca = (1x40)x100 / 100 = 40%
Molar mass of C = 12 g/mol → %C = (1x12)x100 / 100 = 12%
Molar mass of O = 16 g/mol → %O = (3x16)x100 / 100 = 48%
Alternative E is the correct answer.

Freezing point, temperature at which a liquid becomes a solid.
Freezing point depression occurs when the freezing point of a liquid is lowered or depressed by adding another compound to it.
Among the alternatives given, the freezing point of a solution is lowered by increasing the number of solute particles.
Alternative D is the correct answer.

Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute. Colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.
Therefore, from the given alternatives, a colligative property of water is freezing point and boiling point.
Alternative E is the correct answer.

The activity series is a listing of elements in descending order of reactivity.
Given that a reaction will take place between zinc metal and copper sulfate solution forming zinc sulfate, means that zinc is listed above copper in the activity series of metals; zinc metal will react with copper ions to form zinc ions and copper metal (redox reaction).
Therefore, zinc is more reactive than copper metal.
Alternative C is the correct answer.

A combustion reaction is a type of redox reaction that occurs when a substance combines with oxygen (oxidation number 0) to make oxygen-containing compounds of other elements (oxidation number of oxygen -2) in the reaction.
The oxidation number of O decreases from 0 to −2, which means that O gains electrons and is reduced during the reaction.
In combustion, the oxygen (O₂) is reduced and the other elements are oxidized.
Alternative D is the correct answer.

The equation for dissociation is:
Sn(OH) _2(s) ⇌ Sn²⁺_(aq) + 2OH^-_(aq)
The solubility product expression Ksp = [Sn²⁺][OH^-]²
Alternative C is the correct answer.

Iron (III) fluoride: FeF₃
[Fe] = x
[F] = y
The equation for dissociation is:
FeF_3(s)⇌ Fe³⁺_(aq) + 3F^-_(aq)
K_sp = [Fe³⁺][ F^-]³
K_sp = xy³
Alternative D is the correct answer.

M(butene) = 56 g/mol
M(butene) = C_nH_2n = 56 g/mol
12n + 2n = 56
14n = 56
→ n = 4
Then, the molecular formula of this compound is: C₄H₈
Alternative B is the correct answer.

Caffeine molecular mass = 195 g/mol
49.5% C, 5.15% H, 28.9% N and 16.5 % O
Assume we have 100 g of the compound. Then we have 49.5 g of C, 5.15 g of H, 28.9 g of N and 16.5 g of O
Convert to moles:
Moles of C = 49.5/12 = 4.125 mol
Moles of H = 5.15/1 = 5.15 mol
Moles of N = 28.9/14 = 2.06 mol
Moles of O = 16.5/16 = 1.03 mol
Divide moles by the smallest of the results:
C: 4.125/1.03 = 4
H: 5.15/1.03 = 5
N: 2.06/1.03 = 2
O: 1.03/1.03 = 1
The empirical formula of caffeine is: C₄H₅N₂O.
The empirical formula is the simplest formula of a compound.
The molecular formula, is an integral multiple of the empirical formula → Molecular formula of caffeine = (C₄H₅N₂O)n.
The empirical formula mass = 98 g/mol
The molecular formula mass = 195 g/mol
n = 195/98 = 1.98 ≈ 2
Therefore, the molecular formula of caffeine is: (C₄H₅N₂O)₂ = C₈H₁₀N₄O₂
Alternative D is the correct answer.

n = N / N_A = 1.204 x 10²⁴ / 6.022 x 10²³ = 1.999 mol
Alternative B is the correct answer.

Ethylene C₂H₄ is the simplest alkene (C_nH_2n), an unsaturated hydrocarbon that contain C=C bond as functional group.
The types of bonding present in C₂H₄: a double bond (C=C) and single bonds (4 C-H).

Alternative B is the correct answer.

All alternatives respect the complete combustion reaction concerning the reactants having reacted and the products formed. To choose the correct answer, the number of atoms for each element in the reaction must be the same for both the reactants and the products.
The balanced equation for the complete combustion of ethylene is:
C₂H₄ + 3O₂ → 2CO₂ + 2H₂O (2 C atoms at both sides, 6 O atoms at both sides and 4 H atoms at both sides)
Alternative A is the correct answer.

n_C2H4 = m / M = 45 / 28 = 1.607 mol
As stoichiometry:
n_C2H4 / 1 = n_CO2 / 2 → n_CO2 = 2 x n_C2H4 / 1 = 2 x 1.607 / 1 = 3.214mol
n = m / M → m_CO2 = n_CO2 x M_CO2 = 3.214 x 44 = 141.4 g
Alternative C is the correct answer.

n_C2H4 = m / M = 45 / 28 = 1.607 mol → R_C2H4 = n_C2H4 / 1 = 1.607
n_o2 = V / V_m = 5 / 22.4 = 0.223 mol → R_o2 = n_o2 / 3 = 0.223 / 3 = 0.074
The limiting reagent in this case is oxygen gas. Then, as stoichiometry:
n_O2 / 3 = n_CO2 / 2 → n_CO2 = 2 x n_O2 / 3 = 2 x 0.223 / 3 = 0.148 mol
n_CO2 = 0.148 mol < n_CO2 = 3.214 mol (question 73)
Hence, mass of CO₂ will decrease when n = 0.48 mol.
Alternative C is the correct answer.

An incomplete combustion reaction takes place when there is an insufficient amount of oxygen supply.
During incomplete combustion part of the carbon is not completely oxidized producing soot or carbon monoxide (CO).
Then the products will be carbon monoxide, soot and water vapor.
Alternative D is the correct answer.

According to Le Châtelier, if the pressure is increased, the position of equilibrium will move so that the pressure is reduced again. Pressure is caused by gas molecules hitting the sides of their container. The more gas molecules in the container, the higher the pressure will be. The system can reduce the pressure by reacting in such a way as to produce fewer molecules.
In reference to the given equilibrium reaction:
C_(s) + H₂O_(g) ↔ CO_(g) + H_2(g) The number of moles of gaseous products (2) are more than the number of moles of gaseous reactants (1).
Then, an increase in pressure, will shift the equilibrium in the reverse direction.
Alternative A is the correct answer.

The value of the equilibrium constant in a reversible reaction is not affected by the changes in concentrations of reactants and products.
The only thing that changes an equilibrium constant is a change of temperature. Hence, the equilibrium constant remains the same.
Alternative E is the correct answer.

The reaction given: 2SO_3(g) ↔ 2SO_2(g) + O_2(g)
The equilibrium constant expression K_c for the reaction given is equal to the ratio of the equilibrium product concentrations over the equilibrium reactant concentrations each raised to the power of their stoichiometric coefficients.
K_c = [SO₂]² [O₂] / [SO₃]²
Alternative B is the correct answer.

It requires energy for a solid to melt into a liquid. Melting is an endothermic reaction.
An endothermic reaction is a reaction where thermal energy is taken in from the surroundings so the temperature of the surroundings decreases.
Alternative B is the correct answer.

Change in thermal energy = mass × specific heat capacity × change in temperature.
ΔT = T₂ – T₁ = 25 – 10 = 15 ^oC
m_(s) = 40 kg
Change in thermal energy Q = 30000 J
The specific heat of this substance
C_(s) = Q / m_(s) x ΔT = 30000 / 40 x 15 = 50 J.kg^-1 .°C^-1
Alternative B is the correct answer.

Word equation:
Bromine + Potassium iodide →Potassium bromide + Iodine
Skeleton equation using chemical formulas:
Br + KI → KBr + I₂
Balanced equation:
2Br + 2KI → 2KBr + I₂
Then, the balancing coefficient for iodine produced is 1 and the symbol of iodine produced is I₂
Alternative E is the correct answer.

Solid phosphorus: P_(s)
Oxygen gas: O_2(g)
Diphosphorus pentoxide: P₂O_5(s) (di: 2 – pent: 5)
Word equation:
Solid phosphorus + Oxygen gas → Diphosphorus pentoxide
Balanced equation:
2P_(s) + 5 / 2 O_2(g)→ P₂O_5(s)
Alternative C is the correct answer.

He, Ne, Ar He: Period 1; Group 8A
Ne: Period 2; Group 8A
Ar: Period 3; Group 8A
The three elements are noble gases located in the same Group 8A but in different periods.
Atomic radius increases from top to bottom within a group.
Therefore, the order represents an increasing in atomic radius of He < Ne < Ar.
Alternative C is the correct answer.

A polymer can be made up of many repeating units, which are small monomer molecules that have been covalently bonded. Plastic is a type of synthetic polymer.
A polymerization reaction starts with a primary ingredient (monomer), such as ethylene.
Alternative C is the correct answer.

A conjugate acid is formed when a proton is accepted by a Bronsted base, while a conjugate base is formed when a proton is donated by a Bronsted acid. In the given equation, NH₄⁺ is the conjugate acid of NH₃ base. OH^- is the conjugate base of H₂O acid.
Alternative B is the correct answer.